She jumps off a waterfall!! That should pretty much sum it all up!

and pocahontas

and Mulan!

and pocahontas

Mulan, Pocahontas, and Belle.

uh she went to war for her father!

Yeah, I mean she hangs around with a tiger!

Ariel, Mulan and Pocahontas. Ariel explored a world entirely different from her despite being emotionally abused and punished by her prejudiced father on regular basis because of it and because of Ariel's desire to be more open minded and not as prejudiced as him about people he didn't even know. Later she gave up everything and risked her freedom in order to fulfill her dream of being a part of human world and be with the one she loved. She pshycically confronted Ursula when the latter had the most powerful weapon in the world in order to not let her kill Eric. I don't think any princess is more brave than Ariel, although Mulan is VERY close to that.

Ariel because she left her world and Mulan because she turned into a boy to fight for her country

Oh, yes